Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $59.37   3.592%   $61.5026   $61.50   $61.50   $61.50  
  Purchase #2 $167.40   5.198%   $176.1015   $176.10   $176.10   $176.10  
  Purchase #3 $207.51   5.774%   $219.4916   $219.49   $219.50   $219.50  
  Purchase #4 $244.40   3.761%   $253.5919   $253.59   $253.60   $253.60  
  Purchase #5 $108.46   7.500%   $116.5945   $116.59   $116.60   $116.60  
  Purchase #6 $231.57   12.347%   $260.1619   $260.16   $260.15   $260.20  
  Purchase #7 $172.65   11.207%   $191.9989   $192.00   $192.00   $192.00  
  7 purchase totals = $1,191.36       $1,279.4429   $1,279.43   $1,279.45   $1,279.50